rcu: Provide optional RCU-reader exit delay for strict GPs
The goal of this series is to increase the probability of tools like
KASAN detecting that an RCU-protected pointer was used outside of its
RCU read-side critical section. Thus far, the approach has been to make
grace periods and callback processing happen faster. Another approach
is to delay the pointer leaker. This commit therefore allows a delay
to be applied to exit from RCU read-side critical sections.
This slowdown is specified by a new rcutree.rcu_unlock_delay kernel boot
parameter that specifies this delay in microseconds, defaulting to zero.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 60e2c6e..c532c70 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4128,6 +4128,15 @@
This wake_up() will be accompanied by a
WARN_ONCE() splat and an ftrace_dump().
+ rcutree.rcu_unlock_delay= [KNL]
+ In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
+ this specifies an rcu_read_unlock()-time delay
+ in microseconds. This defaults to zero.
+ Larger delays increase the probability of
+ catching RCU pointer leaks, that is, buggy use
+ of RCU-protected pointers after the relevant
+ rcu_read_unlock() has completed.
+
rcutree.sysrq_rcu= [KNL]
Commandeer a sysrq key to dump out Tree RCU's
rcu_node tree with an eye towards determining
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1761ff4..2f1de27 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -430,6 +430,12 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
return !list_empty(&rnp->blkd_tasks);
}
+// Add delay to rcu_read_unlock() for strict grace periods.
+#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
+static int rcu_unlock_delay;
+module_param(rcu_unlock_delay, int, 0444);
+#endif
+
/*
* Report deferred quiescent states. The deferral time can
* be quite short, for example, in the case of the call from
@@ -460,10 +466,12 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
}
t->rcu_read_unlock_special.s = 0;
if (special.b.need_qs) {
- if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
rcu_report_qs_rdp(rdp->cpu, rdp);
- else
+ udelay(rcu_unlock_delay);
+ } else {
rcu_qs();
+ }
}
/*
